1. Field of the Invention
The invention relates to a process for the purification of waste water, referred to as effluent, from dyeing processes.
2. Description of the Prior Art
It has been proposed in U.S. Pat. No. 3,677,940 to add a coagulant comprising heavy metal ions to dyehouse effluent, to form metallic hydroxide therefrom and to remove the metallic hydroxide floc. Similarly in Japenese patent specification No. 45-2052, the addition of ferrous sulphate to waste water is suggested to remove the colour therefrom. U.S. Pat. No. 3,419,493 discloses a process where calcium ions are added. In all these processes, there is a build up of heavy metal ions in the resultant liquid. This is disadvantageous if the liquid is to be recycled to the dyehouse.
German Auslegeschrift No. 1,177,081 discloses a process for the removal of colloidal substances by electrolysis in the presence of wetting agents, using an iron electrode. When conducting experiments according to the description of that German Auslegeschrift, I have found that the solution itself is electrolysed, is electroflotation takes place with the formation of very small bubbles which float off the wetting agent. Thus, the presence of the wetting agent is essential.